1. Field of the Invention
The present invention relates to electronic disabling devices, and more particularly, to electronic disabling devices which generate a time-sequenced, shaped voltage waveform output signal.
2. Description of the Prior Art
The original stun gun was invented in the 1960's by Jack Cover. Such prior art stun guns incapacitated a target by delivering a sequence of high voltage pulses into the skin of a subject such that the current flow through the subject essentially “short-circuited” the target's neuromuscular system causing a stun effect in lower power systems and involuntary muscle contractions in more powerful systems. Stun guns, or electronic disabling devices, have been made in two primary configurations. A first stun gun design requires the user to establish direct contact between the first and second stun gun output electrodes and the target. A second stun gun design operates on a remote target by launching a pair of darts which typically incorporate barbed pointed ends. The darts either indirectly engage the clothing worn by a target or directly engage the target by causing the barbs to penetrate the target's skin. In most cases, a high impedance air gap exists between one or both of the first and second stun gun electrodes and the skin of the target because one or both of the electrodes contact the target's clothing rather than establishing a direct, low impedance contact point with the target's skin.
One of the most advanced existing stun guns incorporates the circuit concept illustrated in the FIG. 1 schematic diagram. Closing safety switch S1 connects the battery power supply to a microprocessor circuit and places the stun gun in the “armed” and ready to fire configuration. Subsequent closure of the trigger switch S2 causes the microprocessor to activate the power supply which generates a pulsed voltage output on the order of two thousand volts which is coupled to charge an energy storage capacitor up to the two thousand volt power supply output voltage. Spark gap “Gap 1” periodically breaks down, causing a high current pulse through transformer T1 which transforms the two thousand volt input into a fifty thousand volt output pulse.
Taser International of Scottsdale, Ariz., the assignee of the present invention, has for several years manufactured sophisticated stun guns of the type illustrated in the FIG. 1 block diagram designated as the Taser® Model M18 and Model M26 stun guns. High power stun guns such as these Taser International products typically incorporate an energy storage capacitor having a capacitance rating of from 0.2 microfarads at two thousand volts on a light duty weapon up to 0.88 microFarads at two thousand volts as used on the Taser M18 and M26 stun guns.
After the trigger switch S2 is closed, the high voltage power supply begins charging the energy storage capacitor up to the two thousand volt power supply peak output voltage. When the power supply output voltage reaches the two thousand voltage spark gap breakdown voltage. A spark is generated across the spark gap designated as “Gap 1.” Ionization of the spark gap reduces the spark gap impedance from a near infinite impedance level to a near zero impedance and allows the energy storage capacitor to almost fully discharge through step up transformer T1. As the output voltage of the energy storage capacitor rapidly decreases from the original two thousand volt level to a much lower level, the current flow through the spark gap decreases toward zero causing the spark gap to deionize and to resume its open circuit configuration with a near infinite impedance. This “reopening” of the spark gap defines the end of the first fifty thousand volt output pulse which is applied to output electrodes designated in FIG. 1 as “E1” and “E2.” A typical stun gun of the type illustrated in the FIG. 1 circuit diagram produces from five to twenty pulses per second.
Because a stun gun designer must assume that a target may be wearing an item of clothing such as a leather or cloth jacket which functions to establish a one quarter inch to one inch air gap between stun gun electrodes E1 and E2 and the target's skin, stun guns have been required to generate fifty thousand volt output pulses because this extreme voltage level is capable of establishing an arc across the high impedance air gap which may be presented between the stun gun output electrodes E1 and E2 and the target's skin. As soon as this electrical arc has been established, the near infinite impedance across the air gap is promptly reduced to a very low impedance level which allows current to flow between the spaced apart stun gun output electrodes E1 and E2 and through the target's skin and intervening tissue regions. By generating a significant current flow within the target across the spaced apart stun gun output electrodes, the stun gun essentially short circuits the target's electromuscular control system and induces severe muscular contractions. With high power stun guns, such as the Taser M18 and M26 stun guns, the magnitude of the current flow across the spaced apart stun gun output electrodes causes numerous groups of skeletal muscles to rigidly contract. By causing high force level skeletal muscle contractions, the stun gun causes the target to lose its ability to maintain an erect, balanced posture. As a result, the target falls to the ground and is incapacitated.
The “M26” designation of the Taser stun gun reflects the fact that, when operated, the Taser M26 stun gun delivers twenty-six watts of output power as measured at the output capacitor. Due to the high voltage power supply inefficiencies, the battery input power is around thirty-five watts at a pulse rate of fifteen pulses per second. Due to the requirement to generate a high voltage, high power output signal, the Taser M26 stun gun requires a relatively large and relatively heavy eight AA cell battery pack. In addition, the M26 power generating solid state components, its energy storage capacitor, step up transformer and related parts must function either in a high current relatively high voltage mode (two thousand volts) or be able to withstand repeated exposure to fifty thousand volt output pulses.
At somewhere around fifty thousand volts, the M26 stun gun air gap between output electrodes E1 and E2 breaks down, the air is ionized, a blue electric arc forms between the electrodes and current begins flowing between electrodes E1 and E2. As soon as stun gun output terminals E1 and E2 are presented with a relatively low impedance load instead of the high impedance air gap, the stun gun output voltage will drop to a significantly lower voltage level. For example, with a human target and with about a ten inch probe to probe separation, the output voltage of a Taser Model M26 might drop from an initial high level of fifty-five thousand volts to a voltage on the order of about five thousand volts. This rapid voltage drop phenomenon with even the most advanced conventional stun guns results because such stun guns are tuned to operate in only a single mode to consistently create an electrical arc across a very high, near infinite impedance air gap. Once the stun gun output electrodes actually form a direct low impedance circuit across the spark gap, the effective stun gun load impedance decreases to the target impedance-typically a level on the order of one thousand Ohms or less. A typical human subject frequently presents a load impedance on the order of about two hundred Ohms.
Conventional stun guns have by necessity been designed to have the capability of causing voltage breakdown across a very high impedance air gap. As a result, such stun guns have been designed to produce a fifty thousand to sixty thousand volt output. Once the air gap has been ionized and the air gap impedance has been reduced to a very low level, the stun gun, which has by necessity been designed to have the capability of ionizing an air gap, must now continue operating in the same mode while delivering current flow or charge across the skin of a now very low impedance target. The resulting high power, high voltage stun gun circuit operates relatively inefficiently yielding low electro-muscular efficiency and with high battery power requirements.